An aldose is a sugar represented by the following structure, viz.: CH.sub.2 OH--(CHOH).sub.n --CHO. An aldonic acid is a sugar derivative formed by oxidizing an aldose to produce a compound represented by the following structure, viz.: CH.sub.2 OH--(CHOH).sub.n --COOH. The carboxylic acid defines the C(1) position of aldonic acid. A 2-ketoaldonic acid is a sugar derivative represented by the following structure, viz.: CH.sub.2 OH--(CHOH).sub.n-1 --CO--COOH, i.e., the 2-ketoaldonic acid includes a carbonyl group at the C(2) position. The present invention is directed to the synthesis of 2-ketoaldonic acids and 2-ketoaldonic acid derivatives. 2-Ketoaldonic acid derivatives include deoxy derivatives and conventional sugar substituents at positions other than the C(1) and C(2) positions.
2-Ketoaldonic acids are conventionally synthesized by an aldolase catalyzed aldol condensation reaction involving pyruvate and an aldose. The enzyme catalyzed aldol reaction proceeds through two steps represented as follows: EQU Enzyme+CH.sub.3 --CHO--COOH.revreaction.Enzyme.multidot.CH.sub.2- --COH--COOH
then EQU Enzyme.multidot.CH.sub.2- --COH--COOH+CH.sub.2 OH--(CHOH).sub.n-3 --COH.revreaction.Enzyme+CH.sub.2 OH--(CHOH).sub.n-1 --CO--COOH
In the first step, pyruvate is bound to the aldolase enzyme and undergoes an enolization reaction. In the second step, the nucleophilic enol attacks the carbonyl group of the aldose to form a condensation product, viz. 2-ketoaldonic acid.
Each of the above steps involves an equilibrium reaction. In each case, the forward reaction is favored by addition of an excess of pyruvate. Unfortunately, it can be difficult to isolate the product from the excess of pyruvate. What is needed is a method for producing 2-ketoaldonic acid using the aldolase condensation reaction wherein the product is not contaminated by an excess of pyruvate.